I. Field of Invention
The invention relates to a method for inactivating pathogens such as bacteria and viruses in donor blood (blood), blood plasma (plasma) and/or erythrocyte concentrates (ECs) by photodynamic treatment and/or irradiation with ultraviolet light.
II. Description of the Related Art
It is known that therapeutic use of blood and blood preparations entails the risk of infecting the recipients with viruses and bacteria. Examples include viral hepatitis B (HBV) and hepatitis C (HCV) as well as the AIDS pathogens HIV-1 and HIV-2. The risk always exists when no step is taken for inactivation and/or elimination of pathogens during the production of such preparations.
There have been a number of efforts to decontaminate blood preparations by photodynamic methods. The principle is based on light treatment of the respective product in the presence of a photoactive substance (a photosensitizer). The incident light must include a wavelength range which is absorbed by the photosensitizer and by which it can be activated. The absorbed energy is either transferred directly to the respective target structure (e.g. the nucleic acid or surface proteins of a virus), which is thereby destroyed, or is transferred to dissolved oxygen molecules, which are thereby activated. This results in formation of singlet oxygen, which has a strong virucidal and bactericidal activity.
The photosensitizer used ideally has a high affinity for essential components of viruses and other pathogens, e.g. for their nucleic acids, and little or no affinity for the constituents of a preparation that is to be decontaminated. As a result of the photodynamic treatment, in this case the pathogens are inactivated while the product activity is retained. For example, methylene blue, a phenothiazine dye, has been described as a suitable photosensitizer for treatment of plasma. Riboflavin (vitamin B2) is used for decontamination of platelet concentrates, and phthalocyanines have been tested for decontamination of ECs. However, methods for photodynamic inactivation of pathogens in ECs have not yet gone beyond the laboratory scale.
This is true to an even greater extent for blood itself. One of the main reasons for this is to be sought in the fact that the incident light must have a certain intensity to be able to activate the photosensitizer used and the blood and ECs have a very low permeability for light of that wavelength. This problem of course also occurs with plasma, although not to the same extent.
It is also known that it is possible to inactivate pathogens by simply irradiating specimens with to ultraviolet (UV) light of a short wavelength, i.e. in the wavelength range between approximately 200 nm and 320 nm, in particular 200 nm to less than 300 nm (UVB and UVC). Above 320 nm, the energy of the radiation is too low to inactivate microorganisms and viruses. In comparison with chemical, photochemical and photodynamic methods of pathogen inactivation, mere irradiation with UV light essentially has the advantage of being effective for itself alone and not requiring the addition of reactive chemicals or photoactive substances.
UVC is the most effective for direct inactivation of pathogens. However, it has the disadvantage that it can penetrate through solutions containing proteins such as plasma and/or cloudy suspensions (e.g. blood and ECs) only to a very low depth of penetration. UVC was used during the Second World War and shortly thereafter for sterilizing plasma and albumin solutions, especially to inactivate hepatitis viruses. At that time, the procedure was to pass a solution as a thin film in a flow-through apparatus past a UVC light source. This method did not prove to be reliable enough and was given up (N. R. Kallenbach, P. A. Cornelius, D. Negus, et al. Inactivation of viruses by ultraviolet light. Curr. Stud. Hematol Blood Transfus. 1989, 56, 70-82).
Methods that operate according to the same principle but have been developed further are being used today for sterilizing therapeutic plasma protein preparations. In all cases, the aim is to treat larger volumes, i.e. plasma pools and/or protein solutions of a few hundred liters or even more (H. Hart, K. Reid, W. Hart. Inactivation of viruses during ultraviolet light treatment of human intravenous immunoglobulin and albumin. Vox Sang 1993; 64(2):82-88 and S. Chin, B. Williams, P. Gottlieb, et al. Virucidal short wavelength ultraviolet light treatment of plasma and factor VIII concentrate: protection of proteins by antioxidants; Blood 1995; 86(11):4331-4336).
The aforementioned flow-through apparatuses are not suitable for sterilizing multiple individual units from blood donors, plasma or ECs having volumes of up to a few hundred mL. However, this is precisely what is needed in everyday practice at a blood bank.
UVB is both microbiocidal and virucidal, although not to the same extent as UVC. It penetrates into solutions containing protein and cloudy suspensions somewhat better than UVC, but its depth of penetration in plasma, for example, is in the range of only a few millimeters.
Plasma and ECs are usually isolated from individual blood donations but are also obtained from individual donors by machine apheresis. The volume of the preparations is generally between approximately 200 and 350 mL. The volume of blood donations is usually between 450 and to 500 mL. The preparations are either deep frozen (plasma) in flat plastic bags or are stored at approximately 4° C. (blood donations, ECs).
It would be desirable to sterilize these preparations in such bags but the problem encountered here, as already mentioned, is that they are virtually impermeable for UV light, and blood and ECs are also impermeable for visible light.